How Does Your Body React When You Smoke?

Long-term addiction to smoking dramatically shortens life spans and diminishes qualify of life for people who get hooked, and the National Institute on Drug Abuse (NIDA) estimates that 12 million people died from tobacco-related causes between 1964 and 2004. The addictive nicotine in cigarettes acts as both a depressant and a stimulant, so lighting up can both relax and perk up smokers, but beyond these immediate effects, that simple act has serious impacts on a smoker's body, affecting cardiovascular and pulmonary health, immune response and brain chemistry.

Cardiovascular Disease

• A single puff from a cigarette causes physiological changes in the human circulatory system, constricting blood vessels and raising heart rates and blood pressure. Changes in blood clotting heighten the risk of stroke or heart attack, and smoking also upsets the balance between HDL ("good") cholesterol and LDL ("bad") cholesterol, causing faster accumulation of arterial plaque that blocks arteries and intensifies the stress on the circulatory system. Because of these overlapping effects, the Centers for Disease Control and Prevention (CDC) estimates that smoking increases stroke and heart disease risks by two to four times.

Lung Disease

• Most smokers know that tobacco smoke dramatically increases the risk of lung cancer, but the habit also causes other serious medical conditions. Doctors also associate it with chronic obstructive pulmonary disease (COPD), a complex of illnesses that includes emphysema and chronic bronchial inflammation. Dawn Milner describes its progression as a smoker gradually loses lung function: "Shortness of breath at first on exercise, later after simple non-strenuous activities, and finally at rest."

  Smoking also destroys cilia in the respiratory system, raises pneumonia risk and severity and causes lung scarring that prevents normal expansion and contraction during breathing.

Immune Responses and Cancer

• A burning cigarette releases gases and particulates containing thousands of chemicals, including 70 known carcinogens such as formaldehyde, benzyne, arsenic and hydrogen cyanide. The relationship between smoking and cancer goes beyond simple cause-and-effect, however. According to the Surgeon General, "smoking can cause cancer and then block your body from fighting it." Smoking triggers overproduction of white blood cells, which puts unusual stress on the immune system and diminishes its ability to mobilize against the cancer cells growing in even healthy human bodies. Because of this overall effect on immune response, smoking causes cancers in parts of the body without any obvious connection to the respiratory system, including the bladder, cervix, kidney, stomach and uterus.

Addiction

• Nicotine, the primary addictive substance in tobacco, has profound effects on body chemistry and mood. It causes increased production of adrenaline as well as dopamine, a neurotransmitter associated with sensations of pleasure and addictive behavior. According to the NIDA, "long-term brain changes induced by continued nicotine exposure result in addiction -- a condition of compulsive drug seeking and use." Nicotine addictions are notoriously difficult to overcome. A 2009 NIDA research report estimated that 85 percent of regular users give up on quitting attempts within a week of butting out.

Other Health Effects

• Smokers face an array of other health consequences, many of them serious. They have an elevated risk of developing insulin-dependent (Type 2) diabetes, which carries an additional risk of serious health problems ranging from heart disease to eye problems. Second-hand smoke increases disease risks for passive smokers, or people who do not themselves smoke but have regular exposure to smoke. The risks have proven especially serious for infants and children, and studies link tobacco smoke to childhood asthma and Sudden Infant Death Syndrome. Smoking by pregnant women also elevates the risk of miscarriage, low birth weight and even learning disabilities.